After studying medicine at Bellevue Hospital Medical College, he worked at a sanitarium in Battle Creek, Michigan, advocating good health through a strict vegetarian diet. His skills as a surgeon were highly prized, though he frequently donated his services to indigent patients at the clinic. When his nutritionally enhanced foods began to catch on, he and his brother Will formed Sanitas Food Company to produce and sell the dry wheat, rice, and corn flake breakfast cereal that came out of John's laboratory. When feuding caused the brothers to split, Will continued to market the cereals as the W. K. Kellogg Company, while John formed the Battle Creek Food Company to develop and market coffee substitutes and soy milk. He wrote some 50 books to advance his nutritional theories, but never enjoyed the fame and fortune accorded to his estranged brother.